Name and define the process responsible for the ascent of sap.

Transpiration pull is the process which is responsible for the ascent of xylem sap. Transpiration refers to the loss of excess water through the aerial parts of the plant. Numerous tiny pores called stomata present on the surface of the leaves are responsible for evaporation of water as well as the exchange of gases. The water is pulled by the plant from the roots upto the leaves. Some amount of this water is used up by the leaves for photosynthesis. This transpiration pull forms a continuous column of xylem sap along the stem of the plant.

You must have wondered how water reaches up to great heights in tall trees. It is due to this transpiration pull that develops a pulling force which is enough to lift the water column.